In electrophotographic printing, a charge retentive surface, known as a photoreceptor, is electrostatically charged, and then exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on the photoreceptor form an electrostatic charge pattern, known as a latent image, conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder known as "toner." Toner is held on the image areas by the electrostatic charge on the photoreceptor surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate or support member (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is useful for light lens copying from an original or printing electronically generated or stored originals such as with a raster output scanner (ROS), where a charged surface may be imagewise discharged in a variety of ways.
In the process of electrophotographic printing, the step of conveying toner to the latent image on the photoreceptor is known as "development." The object of effective development of a latent image on the photoreceptor is to convey toner particles to the latent image at a controlled rate so that the toner particles effectively adhere electrostatically to the charged areas on the latent image. A commonly used technique for development is the use of a two-component developer, which comprises, in addition to the toner particles which are intended to adhere to the photoreceptor, a quantity of magnetic carrier beads. The toner particles adhere triboelectrically to the relatively large carrier beads, which are typically made of steel. When the developer is placed in a magnetic field, the carrier beads with the toner particles thereon form what is known as a magnetic brush, wherein the carrier beads form relatively long chains which resemble the fibers of a brush. By applying this magnetic brush to a photoreceptor, the electrostatic charge on the photoreceptor will cause the toner particles to be pulled off the carrier beads and onto the photoreceptor.
Another known development technique involves a single-component developer, that is, a developer which consists entirely of magnetized toner. In such a developer, each toner particle has both an electrostatic charge (to enable it to adhere to the photoreceptor) and magnetic properties (to allow the particles to be magnetically conveyed to the photoreceptor). Instead of using magnetic carrier beads to form a magnetic brush, the magnetized toner particles in a single-component system are caused to adhere magnetically to a rotating cylinder known as a developer roll. The developer roll is typically in the form of a cylindrical sleeve which rotates about a stationary magnet assembly. The magnet assembly within the developer roll typically includes a number of magnets arranged in longitudes along the length of the developer roll with generally alternating polarities, so that magnetic lines of flux will extend to the exterior of the roll. Thus, magnetized toner particles adhere to the rotating sleeve by the force of the stationary magnets within the sleeve, and as the sleeve rotates around the magnet, particles adhering to the sleeve will be exposed to an alternating series of magnetic polarities. A metering blade is typically in continuous contact with the sleeve along one longitude of the developer roll so that the toner particles will adhere to the moving sleeve in a thin, uniform coating. When this thin layer of particles is obtained, the developer roll advances the toner particles to a developement zone adjacent the surface of the photoreceptor. In the development zone, the toner particles adhering magnetically to the developer roll are attracted electrostatically to the latent image recorded on the photoreceptor. With this technique, toner particles may be evenly distributed on the latent image.
In the prior art there are numerous modifications to the basic single-component developer system to ensure high copy quality. In U.S. Pat. No. 4,469,427 to Kopp et al., a vacuum device is described for use in removing stray toner particles from the gap between the developer roll and the photoreceptor. U.S. Pat. No. 4,553,829 to Bares discloses a single-component development system wherein the metering blade includes at least one aperture therein through which the toner particles may pass, so that the thickness of the layer of toner particles on the developer roll may be accurately controlled. U.S. Pat. No. 4,523,833 to Jones discloses a metering blade having electrodes defined therein so that the flow of magnetized toner particles on the developer roll may be controlled by means of an induced electric field. U.S. Pat. No. 4,774,541 to Martin et al. discloses a squirrel-cage device for charging toner particles so that the toner particles may be more efficiently conveyed on the developer roll to the photoreceptor.
U.S. Pat. No. 4,779,119 to Kaieda discloses a cleaning blade for use in removing residual toner from a photoreceptor (as opposed to a developer roll) in which a deformable edge portion mounted on a resilient leg engages the moving photoreceptor surface. A pair of elastic side seal members are mounted on the edge portion at locations beyond the the image recording region of the photoreceptor.
One practical problem which has been experienced with developer rolls in single-component systems is the difficulty in managing the behavior of toner particles within the housing of the developement system. Toner particles may have a tendency to migrate to the edges of the developer roll, or may drop from the developer roll and get into other parts of the machine. A particular problem occurs in the areas at the end of a developer roll, where the magnetic force of the stationary magnets within the developer roll may not provide sufficient coverage to maintain the toner particles thereon. It has thus been a common design concern to ensure a tight mechanical seal around the ends of the developer roll. In order to function properly, such a seal must not only prevent the migration of toner particles from the developer roll and subsequently into machine parts, but must also have low friction against the developer roll so there will be little mechanical resistance to decrease the efficiency of the machine as a whole. Perhaps most importantly, such seals must be long-lasting. The most common type of seal currently in use is an adhesive backed cotton felt strip faced with Teflon.RTM. felt; seals of such construction have been known to fail in as few as 3,000 copies. Such failures could result in either toner leaking into machine parts, degradating performance, or causing a visible copy quality defect on copies. Installation of such seals as is known in the prior art is difficult because such seals tend to be dimensionally imprecise and not preformed. Unfortunately, most resilient materials, such as felt, are to an extent porous, and for this reason do not form a reliable barrier to infiltration by toner particles.
It is an object of the present invention to provide a means for sealing the ends of a developer roll which is long-lasting, efficient, and which provides an acceptably small level of mechanical resistance to the motion of the sleeve of the developer roll.